Cluster decays of Be-12 excited states

An experimental study of the helium-cluster decays of the Be-12 excited states has been performed using the Li-9 + Li-7 -> alpha + alpha + He-8 and Li-9 + Li-7 -> alpha + He-6 + He-6 reactions at the Li-9 beam energy of 74.8 MeV. At excitation energies between 10 and 25 MeV, the Be-12 excited states decaying into the He-4 + He-8, He-6 + He-6, and He-6 + He-6*(1.8 MeV, J( pi ) = 2(+)) have been observed. Most of the observed states decaying into the He-4 + He-8 and He-6 + He-6 correspond to previously reported states. The decay to the He-6 + He-6*(1.8 MeV, J( pi ) = 2(+)) channel has been observed for the first time. Two of the five states observed in this new decay channel are also observed in the ground state channel He-6 + He-6, while two may correspond to the He-4 + He-8 decaying states. The states around 13.5 and 20.0 MeV decay to the He-6 + He-6 and He-4 + He-8 channels, while the state around 22.3 MeV decays into all three decay channels examined. This experiment is complementary to all previous studies of the Be-12 cluster states because of the different reaction mechanisms used for the population of the Be-12 cluster states. The observation of the states at high excitations with these exotic decay properties strongly supports the molecular structure of the Be-12 excited states.